Physical Layer Frame Format Design for Wideband Wireless Communications Systems

ABSTRACT

Systems and methods are provided for processing a payload portion of a received signal in a single carrier mode or a multiple carrier mode using a wireless channel receiver based on a portion of the received signal, where a signaling portion of the received signal is a single carrier signal. A single carrier signaling portion is received, and whether the payload portion of the signal is a single carrier signal or a multiple carrier signal is detected from the received single carrier signaling portion. The payload portion of the received signal is demodulated in a single carrier mode if the detecting determines that the payload portion of the received signal is a single carrier signal, and the payload portion of the received signal is demodulated in a multiple carrier mode if the detecting determines that the payload portion of the received signal is a multiple carrier signal. Data from the demodulated payload portion of the received signal is stored in a computer-readable memory.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/410,883 (U.S. Pat. No. 8,358,668), filed on Mar. 25, 2009, whichclaims priority from U.S. Provisional Patent Application No. 61/043,384,filed on Apr. 8, 2008, and entitled “Physical Layer Frame Format Designfor Wideband Wireless Communications Systems”, U.S. Provisional PatentApplication No. 61/044,816, filed Apr. 14, 2008, and entitled “PhysicalLayer Frame Format Design for Wideband Wireless Communications Systems”,and U.S. Provisional Patent Application No. 61/076,453, filed Jun. 27,2008, and entitled “Physical Layer Frame Format Design for WidebandWireless Communications Systems”. The entirety of these disclosures isincorporated herein by reference.

FIELD

The technology described in this patent document relates generally towideband wireless communications, and more particularly to physicallayer frame formats.

BACKGROUND

Continued advances in computer technology increase interest in anddemand for high data rate (e.g., >1 Gbps) wireless communication. Thesehigh data rate communications are often realized through the use of widebandwidths. For example, Gbps data rates are often accomplished usingseveral hundred MHz or several GHz of bandwidth. These large bandwidthsare available around higher carrier frequencies such as the unlicensed60 GHz band. FIG. 1 depicts an example 60 GHz frequency channel plan 30.The plan offers four channels 32 of about 2 GHz each centered near 60GHz. While wide bandwidth channels offer opportunities for large datarates, they are often vulnerable to delay dispersion (delay spread) evenat low range (e.g., less than 10 meters).

There are a wide variety of applications that can take advantage ofwireless communications. Two pervasive applications are high data rateat large range applications and low/moderate data rate at short rangeapplications. These applications have their own advantages anddisadvantages.

In a high data rate at large range application, high data rates areachieved, but the system may have to tolerate a high delay spread. Highdelay spreads increase complexity and power requirements in transmittersand receivers. The higher complexity circuitry tends to have largerspace requirements than short range devices, and the higher power needsare more suited for electrical plug-in devices as opposed to batterydevices. In contrast, low/moderate data rate applications at a shortrange may be line-of-sight applications having a short delay dispersionand lower power requirements. These applications may be realized moreeasily in lower complexity handheld portable wireless systems that areoften sensitive to power consumption.

FIGS. 2A and 2B depict block diagrams of a single carrier transmitter 40and a single carrier receiver 50, respectively. In FIG. 2A, an encoder42 receives input data 44 and encodes the data for transmission. Theoutput of the encoder 42 is propagated to a single carrier modulator 46that integrates the encoded data onto a single carrier for transmissionover an antenna 48. In FIG. 2B, the receiver 50 receives single carrierwireless signals via an antenna 52 and propagates the received signalsto a single carrier demodulator 54. The single carrier demodulator 54extracts data from the received single carrier signal and passes theextracted data to a decoder 56. The decoder 56 decodes the extracteddata and makes the decoded data 58 available to downstream circuitry.

FIGS. 3A and 3B depict block diagrams of a multiple carrier transmitter60 and a multiple carrier receiver 70, respectively. In FIG. 3A, anencoder 62 receives input data 64 and encodes the data for transmission.The output of the encoder 62 is propagated to a multiple carriermodulator 66 that integrates the encoded data onto multiple carriers fortransmission over an antenna 68. In FIG. 3B, the receiver 70 receivesmultiple carrier wireless signals via an antenna 72 and propagates thereceived signals to a multiple carrier demodulator 74. The multiplecarrier demodulator 74 extracts data from the received multiple carriersignals and passes the extracted data to a decoder 76. The decoder 76decodes the extracted data and makes the decoded data 78 available todownstream circuitry.

Data modulation schemes tend to be more compatible with someapplications than others. For example, orthogonal frequency-divisionmultiplexing (OFDM) is a multiple carrier multiplexing scheme that issuitable for sustaining high data rates in channels having a large delaydue to the ease of frequency domain channel equalization. This makesOFDM compatible with the high data rate at large range applicationdescribed above, as OFDM offers relatively simple equalization in a highdelay spread channel, supports a longer range, and supports needed highdata rates.

OFDM disadvantages, however, include a relatively high hardwarecomplexity and low power efficiencies. In a wideband system having ahigh carrier frequency, such as 60 GHz, power amplifier (PA) efficiencyat the transmitter, and analog-to-digital converter (ADC) bit-width atthe receiver are engineering design challenges. Additionally, OFDMintroduces high peak-to-average-ratio (PAPR) in the transmitted andreceived signal waveforms, requiring large headroom for the operatingpoint at the power amplifier and analog-to-digital converter, which mayreduce power amplifier efficiency and increase the complexity ofanalog-to-digital converter design.

It should be noted that the terms multiple carrier (MC) and OFDMmodulation will be discussed throughout this disclosure and are in mostcases interchangeable. Thus, where OFDM is referenced, other multiplecarrier modulation techniques may be used. Similarly, references tomultiple carrier modulations include OFDM implementations.

FIGS. 4A and 4B depict block diagrams of an OFDM transmitter 80 and anOFDM receiver 90, respectively. In FIG. 4A, an encoder 82 receives inputdata 84 and encodes the data for transmission. The output of the encoder82 is propagated to an OFDM modulator 86 that integrates the encodeddata onto multiple carriers for transmission over an antenna 88. In FIG.4B, the receiver 90 receives OFDM wireless signals via an antenna 92 andpropagates the received signals to an OFDM demodulator 94. The MCdemodulator 94 extracts data from the received OFDM signal and passesthe extracted data to a decoder 96. The decoder 96 decodes the extracteddata and makes the decoded data 98 available to downstream circuitry.

In line of sight channels or other applications requiring lower datarates, a single carrier (SC) modulation with a time-domain equalizer isoften sufficient. A single carrier system may offer simplicity inhardware combined with low power requirements and high transmit powerefficiency. Single carrier modulation may present a constant envelopeand/or low peak-to-average ratio easing power amplifier andanalog-to-digital converter design. However, single carrier systemstypically require complicated equalizers for high delay spread channels,effectively limiting the range for high data rate transfers.

SUMMARY

In accordance with the teachings provided herein, systems and methodsare provided for processing a payload portion of a received signal in asingle carrier mode or a multiple carrier mode using a wireless channelreceiver based on a portion of the received signal, where a signalingportion of the received signal is a single carrier signal and thepayload portion of the received signal is a single carrier signal or amultiple carrier signal. The system may include receiving the singlecarrier signaling portion of the received signal and detecting from thesingle carrier signaling portion of the received signal whether thepayload portion of the received signal is a single carrier signal or amultiple carrier signal. The system may then demodulate the payloadportion of the received signal in a single carrier mode if the detectingstep determines that the payload portion of the received signal is asingle carrier signal. The system may demodulate the payload portion ofthe received signal in a multiple carrier mode if the detecting stepdetermines that the payload portion of the received signal is a multiplecarrier signal. The method may store data from the demodulated payloadportion of the received signal in a computer-readable memory.

The detecting step may determine that the payload portion of thereceived signal will be a single carrier signal when the signalingportion or the frame delimiter portion of the received signal contains afirst cover sequence, and the detecting step may determine that thepayload portion of the received signal will be a multiple carrier signalwhen the signaling portion or the frame delimiter portion of thereceived signal contains a second cover sequence. The detecting step maydetermine that the payload portion of the received signal will be asingle carrier signal when the signaling portion or the channelestimation portion of the received signal contains a first spreadingsequence, and the detecting step may determine that the payload portionof the received signal will be a multiple carrier signal when thesignaling portion or the channel estimation portion of the receivedsignal contains a second spreading sequence.

The received signaling portion of the received signal may be part of areceived single carrier preamble, where the received single carrierpreamble further includes a frame delimiter sequence (SFD) that usutilized by the receiver to establish frame timing and may contain asingle carrier channel estimation sequence (CES) that is utilized by thereceiver for channel estimation. A cover sequence in SFD or spreadingsequence in CES may also be used to signal a single carrier or multiplecarrier payload. The receiver may perform channel estimation for boththe single carrier mode and the multiple carrier mode based on thesingle carrier channel estimation sequence. The channel estimation forthe multiple carrier mode may be performed by sampling the singlecarrier channel estimation sequence at a multiple channel mode samplingrate and performing a fast-Fourier transform on the detected samples.

The payload portion of the multiple carrier signal may begin with amultiple carrier channel estimation sequence, where the step ofdemodulating the payload portion of the received signal in a multiplecarrier mode may include performing channel estimation for the multiplecarrier mode based on the multiple carrier channel estimation sequence.The received signaling portion for the received signal may be part of areceived single carrier preamble, and the single carrier preamble maynot include a single carrier channel estimation sequence.

The receiver may perform channel estimation for the multiple carriermode based in part on the single carrier channel estimation signal,where a first estimation for the multiple carrier mode is performed bysampling the single carrier channel estimation sequence at a multiplechannel mode sampling rate and performing a fast-Fourier transform onthe detected samples. The payload portion of the multiple carrier signalmay begin with a multiple carrier channel estimation sequence, where thestep of demodulating the payload portion of the received signal in amultiple carrier mode includes performing a second channel estimationfor the multiple carrier mode based on the multiple carrier channelestimation sequence. A final channel estimation may be calculated basedon the first channel estimation and the second channel estimation.

The signaling portion of the received signal may include a common singlecarrier header portion of the received signal, where the common singlecarrier header portion of the received signal contains physical layerdemodulation/decoding information that includes packet length and pilotinsertion information. The common single carrier header portion maycontain all of the information needed for the receiver to perform singlecarrier or multiple carrier demodulation/decoding.

The detecting step may further include sampling the signaling portion ofthe received signal at a first rate derived from a baseband clock, andthe step of demodulating the payload portion of the received signal in amultiple carrier mode may further include sampling the payload portionof the received signal at a second rate derived from the baseband clock,where the signaling portion of the received signal and the payloadportion of the received signal contain the same carrier frequency. Thefirst rate and the second rate may be the same. The method may furtherinclude performing channel estimation for the multiple carrier modeusing only signals of the received single carrier signaling portion,where the received single carrier signaling portion and the receivedpayload portion in a multiple carrier mode were transmitted using a samedigital filter. The first rate may be about 1.728 GHz, and the secondrate may be about 2.592 GHz.

The signaling portion of the received signal may include a common singlecarrier header portion, where the common single carrier header portionconcludes with one or more single carrier conclusion signals that areknown to the receiver. The payload portion may begin with one or moremultiple carrier start signals that are known to the receiver. The stepof demodulating the payload portion of the received signal in a multiplecarrier mode may further include receiving the multiple carrier payloadportion of the received signal that is transmitted with the same poweras the single carrier signaling portion of the received signal.

The detecting step may further include sampling the signaling portion ofthe received signal at a first rate derived from a baseband clock, wherethe step of demodulating the payload portion of the received signal in amultiple carrier mode further includes sampling the payload portion ofthe received signal at a second rate derived from the baseband clock.The second rate may be 1.5 times as fast as the first rate, and thefirst rate and the second rate may be aligned such that a first sampleat the first rate coincides with a first sample at the second rate, anda third sample at the first rate coincides with a fourth sample at thesecond rate.

The detecting step may further include sampling the signaling portion ofthe received signal at a first rate derived from a baseband clock, wherethe step of demodulating the payload portion of the received signal in amultiple carrier mode further includes sampling the payload portion ofthe received signal at a second rate derived from the baseband clock.The second rate may be 2 times as fast as the first rate, and the firstrate and the second rate may be aligned such that a first sample at thefirst rate coincides with a first sample at the second rate, and asecond sample at the first rate coincides with a third sample at thesecond rate.

The payload portion of the received signal in a single carrier mode maybe received at the same data rate as the signaling portion of thereceived signal. The receiver may perform carrier sensing, AGC/ADCsetting, carrier frequency offset detection, and timing referencedetection using the received single carrier signaling portion of thereceived signal for both the single carrier mode and the multiplecarrier mode.

The received signaling portion of the received signal may be part of asingle carrier preamble, where the received single carrier preamble isimmediately followed by a multiple carrier channel estimation sequence,where the multiple channel estimation sequence is followed by a multiplecarrier channel header. The multiple carrier channel header may befollowed by the multiple carrier payload portion. The multiple carriersignal may be an OFDM signal. The received signal may comply with astandard selected from the group consisting of 802.15.3c, 802.11g, and802.11n.

As another example, a processor-implemented method of processing achannel time allocation portion of a received signal in a single carriermode or a multiple carrier mode using a wireless channel receiver basedon a portion of the received signal, where a signaling portion of thereceived signal is a single carrier signal and the channel timeallocation portion of the received signal is a single carrier signal ora multiple carrier signal may include receiving the single carriersignaling portion of the received signal, and detecting from the singlecarrier signaling portion of the received signal whether the channeltime allocation portion of the received signal is a single carriersignal or a multiple carrier signal. The channel time allocation portionof the received signal may be demodulated in a single carrier mode ifthe detecting step determines that the channel time allocation portionof the received signal is a single carrier signal. The channel timeallocation portion of the received signal may be demodulated in amultiple carrier mode if the detecting step determines that the channeltime allocation portion of the received signal is a multiple carriersignal. Data from the demodulated channel time allocation portion of thereceived signal may be stored in a computer-readable memory.

The signaling portion of the received signal may be received at a firstdata rate, where the received channel time allocation portion of thereceived signal in the multiple carrier mode is received at a seconddata rate that is faster than the first data rate, where the receivedchannel time allocation portion of the received signal in the singlecarrier mode is received at the first data rate. The signaling portionof the received signal may include a beacon portion and a contentionaccess portion, where receiving the signaling portion of the receivedsignal as a single carrier signal prevents collisions by devices that donot support the multiple carrier mode because the devices that do notsupport the multiple carrier mode recognize the signaling portion of thereceived signal.

As a further example, a wireless channel receiver configured to processa payload portion of a received signal in a single carrier mode or amultiple carrier mode based on a portion of the received signal, where asignaling portion of the received signal is a single carrier signal andthe payload portion of the received signal is a single carrier signal ora multiple carrier signal may include an antenna, and a single carrierreceiver configured to receive the single carrier signaling portion ofthe received signal from the antenna. The receiver may include a modedetector configured to determine whether the payload portion of thereceived signal is a single carrier signal or a multiple carrier signalbased on the single carrier signaling portion of the received signal.The receiver may further include a demodulator configured to receive thepayload portion of the received signal from the antenna and demodulatethe payload portion of the received signal in a single carrier mode ifthe mode detector determines that the payload portion of the receivedsignal is a single carrier signal and to demodulate the payload portionof the received signal in a multiple carrier mode if the mode detectordetermines that the payload portion of the received signal is a multiplecarrier signal. The receiver may further include a computer-readablememory configured to store data from the demodulated signal from thedemodulator.

As another example, a transmitter for transmitting a single carrierpayload or a multiple carrier payload may include an antenna and asingle carrier modulator configured to transmit a single carriersignaling portion of a signal. The transmitter may further includeselection logic configured to select between a single carrier mode and amultiple carrier mode. A multiple carrier modulator may be configured totransmit the multiple carrier payload following the transmission of thesingle carrier signaling portion of the signal when the selection logicselects the multiple carrier mode. The single carrier modulator may befurther configured to transmit the single carrier payload followingtransmission of the single carrier signaling portion of the signal whenthe selection logic selects the single carrier mode.

As a further example, a method for transmitting a payload portion of asignal in a single carrier mode or a multiple carrier mode may includetransmitting a single carrier signaling portion of the signal anddetermining whether to send the payload portion of the signal in asingle carrier mode or a multiple carrier mode. The payload portion ofthe signal may be transmitted over multiple carriers if the multiplecarrier mode is selected by the determining step, and the payloadportion of the signal may be transmitted over a single carrier if thesingle carrier mode is selected by the determining step.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an example 60 GHz frequency channel plan.

FIGS. 2A and 2B depict block diagrams of a single carrier transmitterand a single carrier receiver.

FIGS. 3A and 3B depict block diagrams of a multiple carrier transmitterand a multiple carrier receiver.

FIGS. 4A and 4B depict block diagrams of an OFDM multiple carriertransmitter and an OFDM multiple carrier receiver.

FIGS. 5A and 5B depict block diagrams of a single carrier transmitterand a dual mode transmitter.

FIGS. 6A and 6B depict block diagrams of a single carrier receiver and amultiple carrier receiver that includes a packet synchronizer/headerdecoder.

FIGS. 7A and 7B depict a dual mode receiver that includes a packetsynchronizer/header decoder and a second dual mode receiver.

FIG. 8 depicts a superframe structure for IEEE 802.15.3c MAC.

FIG. 9 depicts a single carrier modulated packet.

FIG. 10 depicts an OFDM multiple carrier modulated packet.

FIG. 11 depicts an OFDM multiple carrier modulated packet that includesan OFDM channel estimation sequence.

FIG. 12 depicts a common single carrier preamble.

FIG. 13 is a flow diagram depicting detection of a payload transmissionmode based on a carrier cover sequence.

FIG. 14 is a flow diagram depicting detection of a payload transmissionmode based on a carrier spreading sequence.

FIG. 15 depicts a common single carrier header.

FIG. 16 depicts an OFDM multiple carrier modulated packet that includesan OFDM channel estimation sequence and a header tail in the commonsingle carrier header.

FIG. 17 depicts sample timing where the OFDM clock samples at 1.5 timesas fast as a single carrier clock.

FIG. 18 depicts sample timing where the OFDM clock samples at 2 times asfast as a single carrier clock.

FIG. 19 depicts a transmitter configuration for maintaining a coherentspectrum between a single carrier portion and a multiple carrier portionof a received signal.

FIG. 20 depicts an OFDM multiple carrier modulated packet that includesan OFDM channel estimation sequence that does not include a singlecarrier channel estimation sequence.

FIG. 21 depicts an OFDM multiple carrier modulated packet that issampled at the same rate throughout the single carrier and multiplecarrier portions.

FIGS. 22A and 22B depict a single carrier modulated packet that includesa single carrier header and an OFDM multiple carrier modulated packetthat includes an OFDM header that contains an OFDM channel estimationsequence.

FIG. 23 is a flow diagram for decoding a single carrier mode signal or amultiple carrier mode signal based on a received signaling portion of areceived signal.

FIG. 24 is a flow diagram for a method for transmitting a single carrierpayload or a multiple carrier payload following transmission of a singlecarrier signaling portion of a signal.

FIG. 25 illustrates an exemplary implementation of the presentinvention.

DETAILED DESCRIPTION

Based on the application, at least three types of wideband devices maybe present in a wireless network: 1.) SC-Only devices such as simplehandheld, low-range, low-power devices; 2.) MC-Only devices that targetlonger range and higher data rates that are not as sensitive to powerand complexity as SC-Only devices; and 3.) Dual-Mode devices that takeadvantage of both single carrier modulation and multiple carriermodulation that may control or talk with both single carrier andmultiple carrier devices. Co-existence between these various types ofdevices may be problematic, especially if the devices cannot communicateto each other—e.g., SC-Only devices may not be able to communicate withMC-Only devices.

To alleviate these communications issues, a common preamble/header frameformat may be used for the physical layer that may be utilized by allthree types of devices. Using this common format, any device mayunderstand the preamble/header of any packet. This enables networktraffic to be well-controlled without transmission conflicts. Hardwarecomplexity may also be reduced because any device (including the dualmode device) need only implement one single carrier sense,synchronization, header decoding, or channel estimation mechanism at itsreceiver. The common preamble and header is included in transmissions ofboth single carrier modulated packets and multiple carrier modulatedpackets. The common preamble and header is transmitted in a singlecarrier mode such that all three of the above described wideband devicesmay interpret the preamble and header, and all devices in the networkare designed such that all devices can understand the single carriercommon preamble and header.

FIGS. 5A and 5B depict block diagrams of a single carrier transmitter100 and a dual mode transmitter 110 for transmitting packets accordingto the above described format The single carrier transmitter 100 of FIG.5A includes an encoder 102 that receives data 104 that encodes the datafor transmission. A single carrier modulator 106 receives the output ofthe encoder 102 and modulates the encoded data onto a single carrier.The modulated signal is then transmitted via an antenna 108. The singlecarrier transmitter 100 of FIG. 5A is able to send SC packets accordingto the common preamble/header frame format utilizing the same hardwareas the SC-Only transmitter described with reference to FIG. 2A. Thesingle carrier transmitter 100 transmits the common preamble/header viathe antenna 108 and follows the common preamble/header with a singlecarrier payload containing the encoded data.

FIG. 5B depicts a dual-mode transmitter 110 for transmitting packetsaccording to the above described format. The dual-mode transmitter 110is capable of transmitting both single carrier signals and multiplecarrier signals, such as OFDM modulated signals, according to the commonpreamble/header format. The dual-mode transmitter 110 includes anencoder 112 that receives and encodes data 114 for transmission. In boththe single carrier mode and multiple carrier mode, the commonpreamble/header is modulated utilizing a single carrier modulator 116and transmitted via the antenna 118. In a single carrier mode, encodedpayload data from the encoder 112 is modulated using the single carriermodulator 116 and transmitted via the antenna 118 following transmissionof the common preamble/header. In a multiple carrier mode, the commonpreamble/header is modulated by the single carrier modulator 116 andtransmitted via the antenna 118 in a similar fashion as in the singlecarrier mode. However, in the multiple carrier mode, the encoded payloaddata is modulated by the multiple carrier modulator 120 and transmittedvia the antenna 118 following transmission of the single carrier commonpreamble/header.

FIGS. 6A and 6B respectively depict block diagrams of a single carrierreceiver 130 and a multiple carrier receiver 140 that includes a packetsynchronizer/header decoder. Both of the depicted receivers are capableof understanding the single carrier common preamble/header. The receiver130 of FIG. 6A is an SC-Only receiver similar to the receiver describedwith reference to FIG. 2B. The SC-Only receiver 130 receives the singlecarrier common preamble/header via an antenna 132 which propagates thecommon preamble/header to a single carrier demodulator 134 whichprocesses the common preamble/header. The common preamble/headeridentifies whether the following payload portion of the packet is asingle carrier signal or multiple carrier signal. If the commonpreamble/header identifies a single carrier payload, the single carrierdemodulator 134 receives the payload via the antenna 132, demodulatesthe payload, and passes the demodulated payload to the decoder 136,which decodes the data 138 and makes it available to downstreamcircuitry. If the common preamble/header identifies a multiple carrierpayload, the payload is ignored because the single carrier receiver 130cannot process the multiple carrier payload.

As shown in FIG. 6A, the SC-only device does not need to implement anadditional processing block to support multiple carrier packets. Anysingle carrier modulated packet is a “pure” single carrier packet thatrequires no additional processing. Multiple carrier packets areconstructed with a single carrier modulated preamble and header, so thesingle carrier device can decode the header and know theduration/destination of the multiple carrier packet.

Referring to FIG. 6B, the MC-Only receiver 140 is configured tounderstand the single carrier common preamble/header. The MC-Onlyreceiver 140 receives the single carrier common preamble/header via anantenna 142. The received single carrier common preamble/header isprocessed by a packet synchronizer/header decoder 144 that detectswhether the payload portion that follows will be a single carrier signalor multiple carrier signal as well as several characteristics of theincoming payload signal. The packet synchronizer/header decoder 144forwards these detected parameters to a multiple carrier demodulator146. If the packet synchronizer/header decoder detects that the incomingpayload portion of the packet is a single carrier signal, the payload isignored as the multiple carrier demodulator 146 is not capable ofprocessing the single carrier payload. However, if the commonpreamble/header identifies a multiple carrier payload, the multiplecarrier demodulator 146 receives the payload via the antenna 142 asshown at 148, demodulates the payload, and passes the demodulatedpayload to the decoder 150, which decodes the data 152 and makes thedata available to downstream circuitry. As shown in FIG. 6B, the MC-onlyreceiver 140 requires only one additional, simple packet synchronizationand header decoding receiver block for extracting all the physical layerinformation for multiple carrier demodulation/decoding.

FIGS. 7A and 7B depict a dual mode receiver 160 that includes a packetsynchronizer/header decoder and a second dual mode receiver 180. Both ofthe depicted receivers are capable of understanding the single carriercommon preamble/header. The dual mode receiver 160 of FIG. 7A receivesthe single carrier common preamble/header via an antenna 162. Thereceived preamble/header is propagated to a single carrier demodulator164 and a packet synchronizer/header decoder 166. Both the singlecarrier demodulator 164 and the packet synchronizer/header decoder 166process the received preamble/header to detect whether the followingpayload will arrive via a single carrier signal or a multiple carriersignal and to determine parameters of the signal and payload. If theincoming payload is a single carrier payload, the single carrierdemodulator 164 extracts the payload from the single carrier signal andpasses the payload to the decoder 172 which makes the decoded data 174available to downstream circuitry. If the incoming payload is a multiplecarrier payload, the packet synchronizer/header decoder 166 forwardsparameters of the incoming signal and payload to the multiple carrierdemodulator 168. The multiple carrier demodulator 168 receives themultiple carrier signal as shown at 176 and extracts the payload fromthe multiple carrier signal. The extracted payload is then propagated tothe decoder 172 which makes decoded data 174 available to downstreamcircuitry.

Referring to FIG. 7B, the dual mode receiver 180 receives the singlecarrier common preamble/header via an antenna 182. The commonpreamble/header is processed by the single carrier demodulator 184 whichdetects whether the incoming payload portion of the packet is a singlecarrier signal or multiple carrier signal. If the incoming payload is asingle carrier signal, the single carrier demodulator 184 extracts thepayload and passes the payload data to a decoder 186 which makes thedecoded data 188 available to downstream circuits. If the incomingpayload is a multiple carrier signal, the single carrier demodulatoralerts the multiple carrier demodulator 190 and passes along parametersof the incoming payload and signal as shown at 192. The multiple carrierdemodulator 190 receives the incoming multiple carrier payload as shownat 194. The multiple carrier demodulator 190 extracts the payload fromthe multiple carrier signal and forwards the payload to the decoder 186that makes the decoded data 188 available to downstream circuitry.

As illustrated above, the MC-Only and dual mode receivers require only asmall amount of additional hardware to handle the modified packetformat. The receivers may require two sets of sampling clocks that comefrom the same source clock. Alternatively, the receiver may sample usingthe multiple carrier higher clock rate all through the packet and applydigital interpolation for the lower clock rate segments. The receiversutilize the preamble information for determining carrier sense,frequency offset, timing reference, AGC/ADC setting, and single carrierchannel impulse estimation (at least for demodulating the header).

Utilizing the above described or similar transmitters and receivers,coexistence between single carrier and multiple carrier hardware may besupported. Even if the modulation format of the incoming packet is notsupported, an SC-Only or MC-Only device may delay its own transmissionsby understanding the preamble/header to avoid collisions. Coexistencemay be guaranteed by transmitting the single carrier commonpreamble/header at a low rate such that all devices in the network canunderstand.

FIG. 8 depicts a superframe structure 200 for IEEE 802.15.3c MAC. Inthis structure 200, the beacon portion 202 and the contention accessperiod portion 204 make up the preamble/header portion 206 that istransmitted using a single carrier signal transmitted at a low commondata rate. This preamble/header portion identifies whether the payloadportion 208 transmitted during the channel time allocation period willbe transmitted via a single carrier signal or multiple carrier signal aswell as parameters of the coming payload and signal such as the physicallayer demodulation/decoding information of the payload portion. Areceiver determines the characteristics of the incoming payload portion208 of the signal and properties of the incoming signal to prepare forreceipt and demodulation of the signal.

FIGS. 9-11 depict example frames that contain common single carrierpreambles/headers. FIG. 9 depicts a single carrier modulated packet 210.The single carrier modulated packet 210 begins with a common singlecarrier preamble 212 followed by a common single carrier header 214. Thesingle carrier preamble/header portions 212, 214 are followed by asingle carrier physical service data unit (PSDU) 216 that may also bereferred to as a single carrier payload portion 216. As illustrated at218, the entire single carrier modulated packet 210 may be sampled atthe receiver by the same single carrier sampling clock.

FIG. 10 depicts an OFDM multiple carrier modulated packet 220 thatincludes a single carrier preamble/header portion. The packet beginswith a common SC preamble 222 and a common single carrier header 224.The common single carrier preamble/header portions 222, 224 may besampled by the single carrier sampling clock as indicated at 226. Thecommon single carrier preamble/header portions 222, 224 are followed byan OFDM PSDU payload portion 228. This multiple carrier payload portion228 may be sampled by a higher rate OFDM sampling clock as indicated at230. This change in sampling rate from the slower single carriersampling clock 226 to the OFDM sampling clock 230 introduces a clockswitch 232 which may be addressed as will be discussed herein below.

FIG. 11 depicts an OFDM multiple carrier modulated packet 240 thatincludes an OFDM channel estimation sequence. The packet begins with acommon single carrier preamble 242 and a common single carrier header244. The common single carrier preamble/header portions 242, 244 may besampled by the single carrier sampling clock as indicated at 246. Thecommon single carrier preamble/header portions 242, 244 are followed byan OFDM payload portion 248. The OFDM payload portion 248 may be sampledby a higher rate OFDM sampling clock as indicated at 250. This change insampling rate from the slower single carrier sampling clock 246 to theOFDM sampling clock 250 introduces a clock switch 252 as was describedwith reference to FIG. 10. The payload portion 248 of the OFDM packet240 includes the PSDU data portion 254 as well as an OFDM channelestimation sequence (CES) portion 256. The CES portion 256 enables anOFDM demodulator to further calibrate for the incoming data portion 254of the packet as will be described further herein below.

As noted with reference to FIGS. 10 and 11, the single carrier andmultiple carrier portions of a packet may be sampled at different ratesto take advantage of benefits and limitations of the differentmodulation schemes. To avoid out-of-band emission and to fulfill thechannel plan (e.g., as shown in the 60 GHz 802.15.3c plan depicted inFIG. 1), single carrier signals may be transmitted with a sampling clockrate (bandwidth) lower than the overall bandwidth of the assignedbandwidth. This is shown in FIG. 1 at 34 where the single carrierbaseband signal is sampled using a clock of 1.728 GHz. Advancedbaseband/analog pulse shape filtering may also be applied on the SCmodulated baseband signal to further reduce out-of-band emissions and tomaintain the spectrum mask defined by the wireless standard.

In contrast, multiple carrier signals, such as OFDM, may be transmittedusing a higher bandwidth and guard subcarriers (null tones) at the edgesof the inband tones to limit out-of-band emission and maintain thespectrum mask. For example, the OFDM baseband signal may be sampledusing a clock rate of 2.592 GHz, which is 1.5 times the single carriersampling rate. In an OFDM signal, pulse shape filtering is easier torealize due to low subcarrier bandwidth and the presence of guardsubcarriers. This pulse shape filtering may be accomplished using timedomain tapering equivalent to frequency domain convolution, or timedomain convolution maybe used.

FIG. 12 depicts a common single carrier preamble portion 260. The commonsingle carrier preamble portion 260 begins with a signaling portion 262followed by a frame delimiter sequence (SFD) 264. A signaling portionmay include a synchronization portion, a channel estimation portion,and/or a header portion. The frame delimiter sequence 264 may befollowed by a single carrier channel estimation sequence 266.

The synchronization subfield 262 contains signals for synchronizing areceiver with an incoming packet. The synchronization subfield 262 maycontain spreading sequences, such as a Golay sequence of length 128,having pi/2 BPSK modulation (or any other modulation that spreads energyequally in real and imaginary parts of the baseband signal) that areconcatenated repeatedly to help achieve synchronization. The signalingportion 262 may additionally or alternatively contain cover sequencesthat are spread using a spreading sequence. Different cover sequencesmay be used for signaling a receiver about various parameters such as apiconet ID or header rate. Different cover sequences may also be used tosignal the receiver as to whether single carrier modulation or multiplecarrier modulation will be applied to the data payload. If this data isincluded in the signaling portion 262, then the receiver may discoverthe single carrier/multiple carrier mode at the very beginning of thepacket, so that the receiver may set receiving physical layerparameters, such as ADC headroom, ADC precision, AGC gain targets,specific for receiving single carrier data or multiple carrier data.Similarly, different spreading sequences may be used to signal thereceiver whether single carrier modulation or multiple carriermodulation will be applied to modulate the data payload (e.g., the useof different or a pair of complementary Golay sequences identifies theformat of the data payload portion). Additionally, carrier sensing,carrier frequency offset, AGC/ADC setting, and timing reference may bedetermined based on the synchronization subfield. Similarly, differentcover sequences in the SFD portion of the preamble or differentspreading sequences in the CES portion of the preamble may be used tosignal the receiver as to whether single carrier modulation or multiplecarrier modulation will be applied to modulate the data payload.

The frame delimiter sequence 264 is a sequence that establishes frametiming such as the Golay sequence using pi/2 BPSK as in the 802.15.3cdraft standard 2.0. The channel estimation sequence 266 is a sequenceknown to the receiver for single carrier and/or multiple carrier channelestimation such as long complementary Golay sequences with pi/2 BPSK asin the 802.15.3c draft standard 2.0.

FIG. 13 is a flow diagram depicting detection of a payload transmissionmode based on a single carrier cover sequence. A dual mode receiverreceives a single carrier signaling portion of a packet as shown at 272.A determination is made at 274 as to whether a single carrier coversequence is present within the signaling portion that identifies thatthe following data payload portion will be a single carrier signal. Ifthe single carrier data payload cover sequence is in the single carriersignaling portion, the yes branch 276 is taken and the payload portionis demodulated and decoded in a single carrier mode as shown at 278. Ifthe single carrier data payload cover sequence is not in the singlecarrier signaling portion, then the incoming data payload will be amultiple carrier signal and the no branch 280 is taken. The payloadportion is then demodulated and decoded in a multiple carrier mode asshown at 282. Alternatively, the presence of different cover sequencesin the SFD portion may be utilized to detect single carrier or multiplecarrier payload portion transmission.

FIG. 14 is a flow diagram depicting detection of a payload transmissionmode based on a carrier spreading sequence. A dual mode receiverreceives a single carrier signaling portion of a packet as shown at 292.A determination is made at 294 as to whether a single carrier spreadingsequence is present within the signaling portion that identifies thatthe following data payload portion will be a single carrier signal. Ifthe single carrier data payload spreading sequence is in the singlecarrier signaling portion, the yes branch 296 is taken and the payloadportion is demodulated and decoded in a single carrier mode as shown at298. If the single carrier data payload spreading sequence is not in thesingle carrier signaling portion, then the incoming data payload will bea multiple carrier signal and the no branch 300 is taken. The payloadportion is then demodulated and decoded in a multiple carrier mode asshown at 302. Alternatively, different spreading sequences in the CESportion may be utilized for signaling single carrier or multiple carrierpayload portion transmission.

FIG. 15 depicts an example common single carrier header 310. The singlecarrier modulated header contains all of the necessary physical layerdemodulation/decoding information, such as packet length, pilotinsertion information, cyclic prefixes, for both single carrier packetsand multiple carrier packets and may contain the MAC layer header. Thereceiver may obtain MAC header information even if the MAC content inthe payload portion is not decodable, due to an unsupported mode,because all receivers are able to interpret the single carrier headerportion. To increase reliability of header decoding, the common singlecarrier header 310 may be transmitted at a low data rate. The headerillustrated in FIG. 15 is in compliance with the 802.15.3c draft 2.0standard.

As noted with reference to FIGS. 10 and 11, a multiple carrier payloadpacket that begins with a single carrier preamble/header portion mayinclude a jump in sampling frequency between the single carrier portionand multiple carrier portion. This jump may require some compensation atthe transmitters and/or receivers to coherently demodulate and decodethe payload portions.

A first compensation that may be required is compensation to maintaincoherence in carrier frequency at the switch. To accomplish coherence inthe carrier frequency, the transmitter uses the same carrier frequencyacross a multiple carrier payload packet's single carrier and multiplecarrier segments. The same source baseband clock is applied across thetwo segments at the transmitter, where a lower sampling rate forgenerating the single carrier portion of the baseband signal may berealized through interpolation.

Another compensation that may be required is compensation to maintaincoherence in carrier phase at the switch. Spectrum mask/out-of-bandtransmissions may be controlled for the single carrier and multiplecarrier segments of a multiple carrier payload packet through the use ofpulse shaping filters. The phase change at the SC/MC switch point maycause a large out-of-band emission if the phase difference between thelast symbol of the single carrier header and the first sample of themultiple carrier payload portion is large.

One solution is to multiply the whole multiple carrier segment by thephasor of the last symbol of the single carrier header or by a phasorwith a phase close to the phase of the header's last symbol. Forexample, if the header is modulated using pi/2 BPSK and the number ofsymbols in the header is a multiple of 4, then the last symbol is +/−j.Thus, compensation may be achieved by multiplying the multiple carriersegment by j if the last symbol is j or by −j if the last symbol is −j

A second solution is depicted in FIG. 16. FIG. 16 depicts a portion ofan OFDM MC modulated packet 320 that includes an OFDM channel estimationsequence 322 and a header tail 324 in the common single carrier header326. The single carrier header portion 326 includes a tail subfield atthe end of the header (e.g., 4 ones with pi/2 BPSK modulation, so thatthe last symbol is −j). The OFDM MC payload portion 328 of the packet 32then includes a multiple carrier CES symbol 322 at the beginning ofpayload portion (e.g., the OFDM-CES subfield that may be used for OFDMchannel estimation refinement). The out-of-band emissions may beminimized by designating the last symbol of the header tail 324 suchthat it contains a small phase shift to the first OFDM-CES symbol. Thesmall phase shift between the selected final header tail 324 symbol andthe known beginning of the OFDM-CES enables elimination of the spuriousout-of-band emissions caused by larger phase shifts at the boundary.

Another compensation that may need to be implemented for successfultransition from the single carrier to multiple carrier portions of asingle carrier payload packet having a single carrier preamble/header iscompensation to maintain coherence in power at the switch. The singlecarrier and multiple carrier segments may need to be transmitted withthe same power. To compensation for this coherence of power across thesingle carrier segment and multiple carrier segments, the receiver AGCmay be appropriately set based upon parameters determined from thesignaling portion of the common single carrier preamble.

The jump from single carrier sampling to multiple carrier sampling mayalso require compensation to ensure coherence in timing. For example, inthe case of 802.15.3c, OFDM is sampled at 1.5 times the rate of SC. Inother words, the time duration for two clock cycles of the singlecarrier portion is the same time as the duration for 3 clock cycles ofthe OFDM portion. In the example of 802.15.3c, to help ensure asuccessful change from single carrier to OFDM, the time alignment shouldbe guaranteed at each 2 cycle boundary of the single carrier clock.Interpolation may be used for converting the clock rates from the samesource clock.

FIG. 17 depicts sample timing where the OFDM clock 332 samples at 1.5times as fast as a single carrier clock 334. The clocks are aligned suchthat a first pulse 336 of the OFDM clock 332 is aligned with a firstpulse 338 of the single carrier clock 334, and a fourth pulse 340 of theOFDM clock 332 is aligned with a third pulse 342 of the single carrierclock 334 as shown at 344.

FIG. 18 depicts sample timing where the OFDM clock 352 samples at 2times as fast as a single carrier clock 354. In the example of FIG. 18,the OFDM clock 352 begins one single carrier pulse width 356 after thelast single carrier header sample 358 as shown at 360. Alternatively,the OFDM clock could run continuously in a similar fashion as shown inFIG. 17, where a first OFDM pulse would align with a first singlecarrier pulse and a third OFDM pulse would align with a second singlecarrier pulse.

As described above, in a single carrier packet containing a singlecarrier preamble/header portion, the receiver may rely on a CES in thesingle carrier portions as described with reference to FIG. 12, or theMC portion of the packet may contain an SC-CES sub-portion as describedwith respect to FIG. 11. In the case where the receiver uses theinformation of the SC-CES portion to perform both single carrier and MCchannel estimation for both single carrier preamble/header and MCpayload demodulation, a coherent spectrum may be kept across the switchfrom single carrier to multiple carrier.

The SC-CES usually derives a channel impulse response with high accuracydue to the processing gain sampled at the single carrier sampling rate.Using the SC-CES, multiple carrier frequency domain (per-sub-carrier)channel estimation may be obtained by over-sampling the estimatedchannel response to the multiple carrier clock rate and performing afast-Fourier transform (FFT) on the detected samples. The FFT may beapplied directly on the time-domain channel estimate, and the resultantfrequency domain channel estimate may be downsampled (e.g., to 352(336+16) tones). To utilize the SC-CES for multiple carrier channelestimation, the frequency response for single carrier and multiplecarrier may need to be near identical to guarantee the quality of themultiple carrier channel estimate.

An equivalent channel is the combination of the over-the-air channel,analog filters at the transmitter and receiver, and digital (pulseshaping) filters at the transmitter and receiver. The over-the-airchannel and analog filters at the transmitter and receiver are oftencommon between the single carrier and multiple carrier segments.However, the digital filters may be different based on designrequirements of the single carrier and multiple carrier segments.

A first mechanism for maintaining a coherent spectrum across the singlecarrier and multiple carrier portions of a packet is to have the singlecarrier and multiple carrier segments utilize the same digital filter atthe transmitter using the same sampling rate. FIG. 19 depicts atransmitter configuration for maintaining a coherent spectrum between asingle carrier portion and an OFDM or other multiple carrier portion ofa received signal. To accomplish this, both segments 372 may beupsampled to the same rate, as shown at 374, and then the same digitalfilter is applied 376 before entering a digital-to-analog converter(DAC) 378.

A second mechanism is to predetermine and fix digital pulse shapingfilters for the single carrier and multiple carrier segments such thattheir frequency responses (amplitude and phase) on different subcarriersare known by both the transmitter and receiver. While filter amplitudesare often flat over the data subcarriers, this second mechanism maylimit implementation flexibility.

In addition to using the SC-CES to perform channel estimation for themultiple carrier portion of the packet, the multiple carrier portion ofthe packet may contain its own MC-CES. In cases where channel estimationis performed using an MC-CES, compensation to maintain a coherentspectrum as described above is not necessary. In addition, if an MC-CESis utilized and the packet is a multiple carrier payload packet,transmission of the SC-CES may not be necessary. FIG. 20 depicts an OFDMmultiple carrier modulated packet 380 that includes an OFDM channelestimation sequence 382 that does not include a single carrier channelestimation sequence. This is shown at 384 where the common singlecarrier preamble does not contain a CES sub-portion. This can becontrasted with the example common single carrier preamble describedwith reference to FIG. 12 above.

The SC-CES may still need to be applied for packets having a singlecarrier payload. The receiver may be configured to be able to tellwhether a single carrier payload is forthcoming, and thus whether anSC-CES is coming, based on the signaling portion 386 of the commonsingle carrier preamble 384. If the SC-CES is not transmitted, thereceiver may use the signaling portion 386 of the common single carrierpreamble 384 to determine single carrier channel estimation (e.g., byadaptive training as in 802.11b), so that the header can still becorrectly decoded. Because the header may be spread using a highspreading factor, it may be robust against channel estimationinaccuracies that might be caused by removing the SC-CES.

As an additional example, the SC-CES and an MC-CES may be transmitted ina multiple carrier payload packet. A first channel estimate may becalculated for the entire packet based on the SC-CES sub-portion. Asecond channel estimate may also be calculated based on the receivedMC-CES sub-portion of the multiple carrier payload portion. Both ofthese first and second channel estimates may be utilized to generate afinal channel estimate that is used in processing the multiple carrierpayload portion.

FIG. 21 depicts an additional example where an OFDM multiple carrierpacket 390 is sampled at the same rate 392 throughout the SC 394 and MC396 portions. In this example, the 394 and MC 396 portions of the packetutilize the same sampling rate throughout. Both portions may fulfill thespectrum mask defined by the regulation authority through appropriatedigital and analog filtering. In this case no sampling rate switching isrequired between the SC and OFDM portions. The non-appearance of thesampling rate jump between the single carrier portion and OFDM portionof the packet mitigates the need for several of the compensationsdescribed above. Additionally, if the same digital filter is appliedthroughout the transmitted packet at the transmitter, the SC-CES may beused for channel estimation throughout the entire packet. Thus, theOFDM-CES may not be needed, further improving physical layer efficiency.As an alternative, an OFDM-CES may be used without use of an SC-CES. Asa further alternative, both an SC-CES and OFDM-CES may be used to gainreliability.

FIGS. 22A and 22B depict a further example. FIG. 22A depicts a singlecarrier modulated packet 400 that includes a single carrier header. FIG.22B depicts an OFDM multiple carrier modulated packet 406 that includesan OFDM header that contains an OFDM channel estimation sequence. Asshown in FIG. 22A, the single carrier payload packet 400 includes acommon single carrier preamble segment 402 and a single carrier headerportion 404. In this example, a single carrier payload packet is of asimilar form as described above. A variation is shown, however, in themultiple carrier payload packet 406 shown in FIG. 22B. The OFDM multiplecarrier modulated packet 406 of FIG. 22B contains a common singlecarrier preamble portion 408 similar to the one shown in FIG. 22A.However, the OFDM payload packet of FIG. 22B does not include a headerportion of the packet in the single carrier portion of the frame.Instead, the clock switching occurs immediately following the singlecarrier preamble portion 408, as illustrated at 410. An OFDM-CESsub-portion is transmitted followed by an OFDM header portion 412, whichis transmitted during the OFDM portion of the OFDM payload packet 406.The OFDM header 412 is then followed by the OFDM payload portion.

FIG. 23 is a flow diagram for decoding a single carrier mode signal or amultiple carrier mode signal based on a received signaling portion of areceived signal. A single carrier signaling portion of the receivedsignal is received as shown at 422. From the received signaling portion,whether the payload portion of the received signal will be a singlecarrier signal or a multiple carrier signal is detected 424. If a singlecarrier payload is signaled by the signaling portion, then the payloadportion of the signal is demodulated and decoded in a single carriermode 426. In contrast, if a multiple carrier payload is signaled by thereceived signaling portion, then the payload portion is demodulated anddecoded in a multiple carrier mode as shown at 428. The decoded payloadis then stored in a computer readable memory 430.

FIG. 24 is a flow diagram for a method for transmitting a single carrierpayload or a multiple carrier payload following transmission of a singlecarrier signaling portion of a signal. A determination is made whetherto send a payload portion of a signal in a single carrier mode or amultiple carrier mode 442. The transmitter transmits an appropriatesingle carrier signaling portion of the signal as shown at 444. Thesignaling portion may identify whether the following payload portion isa single carrier or multiple carrier payload. If the determination ismade to send a multiple carrier payload, then the payload is transmittedover multiple carriers as shown at 446. In contrast, if a single carrierpayload is to be sent, then the payload is transmitted over a singlecarrier as illustrated at 448.

The above described concepts may be implemented in a wide variety ofapplications including those examples described herein below. Referringto FIG. 25, the present invention may be embodied in a device 480. Thedevice can be a device that receives wireless signals—e.g., a storagedevice, a computer system, a smart phone, a set top box, a cellularphone, a personal digital assistant (PDA), a vehicle, and so on. Thepresent invention may implemented within signal processing and/orcontrol circuits, which are generally identified in FIG. 25 at 484, aWLAN interface and/or mass data storage of the device 480. In oneimplementation, the device 480 receives signals from a source andoutputs signals suitable for a display 488 such as a television and/ormonitor and/or other video and/or audio output devices. Signalprocessing and/or control circuits 484 and/or other circuits (not shown)of the device 480 may process data, perform coding and/or encryption,perform calculations, format data and/or perform any other function asrequired by a particular application.

The device 480 may communicate with mass data storage 490 that storesdata in a nonvolatile manner. Mass data storage 490 may comprise opticaland/or magnetic storage devices for example hard disk drives HDD and/orDVDs. The device 480 may be connected to memory 494 such as RAM, ROM,low latency nonvolatile memory such as flash memory and/or othersuitable electronic data storage. The device 480 also may supportconnections with a WLAN via a WLAN network interface 496.

This written description uses examples to disclose the invention,including the best mode, and also to enable a person skilled in the artto make and use the invention. It should be noted that the systems andmethods described herein may be equally applicable to other frequencymodulation encoding schemes. The patentable scope of the invention mayinclude other examples that occur to those skilled in the art.

1. (canceled)
 2. A processor-implemented method comprising: receiving asignal that includes a preamble and a payload portion, the preamblebeing a single carrier signal, and the payload portion being a singlecarrier signal or a multiple carrier signal; determining from thepreamble whether the payload portion is a single carrier signal or amultiple carrier signal, wherein the payload portion is a single carriersignal if a first cover sequence is included in the preamble, and thepayload portion is a multiple carrier signal if a second cover sequenceis included in the preamble; in response to the payload portion being asingle carrier signal, demodulating the payload portion in a singlecarrier mode; in response to the payload portion being a multiplecarrier signal, demodulating the payload portion in a multiple carriermode; and storing data from the demodulated payload portion in acomputer-readable memory.
 3. The processor-implemented method of claim2, wherein determining from the preamble whether the payload portion isa single carrier signal or a multiple carrier signal comprises:determining from a signaling portion of the preamble whether the payloadportion is a single carrier signal or a multiple carrier signal.
 4. Theprocessor-implemented method of claim 2, wherein determining from thepreamble whether the payload portion is a single carrier signal or amultiple carrier signal comprises: determining from a frame delimitersequence (SFD) of the preamble whether the payload portion is a singlecarrier signal or a multiple carrier signal.
 5. Theprocessor-implemented method of claim 2, wherein the payload portionbegins with a multiple carrier channel estimation sequence, and whereindemodulating of the payload portion includes performing channelestimation for the multiple carrier mode based on the multiple carrierchannel estimation sequence.
 6. The processor-implemented method ofclaim 2, wherein: determining from the preamble whether the payloadportion is a single carrier signal or a multiple carrier signalcomprises sampling the preamble at a first rate that is derived from abaseband clock; and demodulating the payload in a multiple carrier modecomprises sampling the payload portion at a second rate that is derivedfrom the baseband clock.
 7. The processor-implemented method of claim 6,wherein the preamble and the payload portion contain the same carrierfrequency.
 8. The processor-implemented method of claim 7, wherein thefirst rate equals the second rate.
 9. The processor-implemented methodof claim 2, wherein the payload has been transmitted with same power asthe preamble.
 10. The processor-implemented method of claim 2, whereinthe multiple carrier signal is an orthogonal frequency-divisionmultiplexing (OFDM) signal.
 11. The processor-implemented method ofclaim 2, wherein the received signal complies with a standard selectedfrom the group consisting of: 802.15.3c; 802.11g; and 802.11n.
 12. Asystem for processing a signal that includes a preamble and a payloadportion, the preamble being a single carrier signal, and the payloadportion being a single carrier signal or a multiple carrier signal, thesystem comprising: a preamble analyzer configured to receive the signal,and determine from the preamble of the received signal whether thepayload portion is a single carrier signal or a multiple carrier signal,wherein the payload portion is a single carrier signal if a first coversequence is in the preamble, and the payload portion is a multiplecarrier signal if a second cover sequence is in the preamble; ademodulator configured to demodulate the payload portion in a singlecarrier mode in response to the payload portion being a single carriersignal, and demodulate the payload portion in a multiple carrier mode inresponse to the payload portion being a multiple carrier signal; and acomputer-readable memory configured to store data from the demodulatedpayload portion of the received signal.
 13. The system of claim 12,wherein the preamble analyzer is configured to determine whether thepayload portion is a single carrier signal or a multiple carrier signalfrom a signaling portion of the preamble.
 14. The system of claim 12,wherein the preamble analyzer is configured to determine whether thepayload portion is a single carrier signal or a multiple carrier signalfrom a frame delimiter sequence (SFD) of the preamble.
 15. The system ofclaim 12, wherein the payload portion begins with a multiple carrierchannel estimation sequence, and wherein the demodulator is configuredto demodulate the payload portion by performing channel estimation forthe multiple carrier mode based on the multiple carrier channelestimation sequence.
 16. The system of claim 12, wherein the preambleanalyzer is configured to sample the preamble at a first rate that isderived from a baseband clock, and wherein the demodulator is configuredto sample the payload portion at a second rate that is derived from thebaseband clock.
 17. The system of claim 16, wherein the preamble and thepayload portion contain the same carrier frequency.
 18. The system ofclaim 17, wherein the first rate equals the second rate.
 19. The systemof claim 12, wherein the payload portion has been transmitted with samepower as the preamble.
 20. The system of claim 12, wherein the multiplecarrier signal is an orthogonal frequency-division multiplexing (OFDM)signal.
 21. The system of claim 12, wherein the received signal complieswith a standard selected from the group consisting of: 802.15.3c;802.11g; and 802.11n.